Watts H-1200 and recorded simultaneously on the cassette tape recorder. This taped spectrum was then read directly into an XDS-Sigma 2 computer using a 300 character-persecond reproducer. The resultant spectrum, after the transmittance values had been converted to absorbance values, is shown in Figure 2. A five-point smooth, after Savitzky and Golay ( I ) , was imposed on the raw data. A single peak (actually the second one from the left in Figure 2) from this smoothed spectrum is illustrated in Figure 3. Such peaks obviously can be readily integrated, either numerically or by curve-fitting approximations.
Figure 3. Portion of spectrum displayed in Figure 2, showing a single peak and illustrating the quality of the digital spectra obtained in this manner
RECEIVEDfor review January 15, 1971 Accepted March 22, lg71* (1) A. Savitzky and M. J. E. Golay, ANAL.CHEM., 36, 1627 (1964)
Versatile Injection System for Gas Chromatography Glenn E. Pollock, Angelo Margozzi, Ralph Donaldson, and Fritz Woeller Ames Research Center, NASA, Moffet Field, Calij 94035
IN CAPILLARY COLUMN gas chromatography, it is the usual practice to inject samples dissolved in a minute amount of solvent. Quantitation is difficult, especially in cases when all of the concentrate from an isolation technique is to be taken up and injected-e.g., in geochemical studies. We have developed an evaporative injector system which we feel will be of value in cases where solutes are contained in dilute solution. The system can also be used for conventional samples and packed columns. It has no heated valves or O-rings which can leak and cause inaccuracies. Figure 1 is a schematic of the system.
EVAPORATION MODE
SAMPLE INPUT
3-WAY VAL
\RESTRICTOR
INJECT MODE
COIL
GAS OFF 5 W A Y VALVE-,
EXPERIMENTAL
The sample is placed into the injector pot ( B ) through orifice ( A ) . The injector is cold and the carrier gas is off during this operation. After the sample is added to the pot, the carrier gas valve is turned on, as shown in Figure 1, so that the gas passes through line (C) which contains a restrictor to control gas flow. Line (C) leads to the injector pot and sweeps out the solvent through orifice ( A ) . After the solvent is evaporated, the gas is shut off and orifice ( A ) is capped with a l/18-in. Swagelok cap. The injector pot is then flash heated and valve (D)is switched to a position such that carrier gas flows through both lines (C) and ( E ) , sweeping the injector pot ( B ) and carrying the sample onto the column (F). The operations of flash heating and turning on gas flow can be carried out in three different orders. They can be carried out as described above-i.e., simultaneously, flash heated, and then carrier gas on: or in the reverse order. The best mode will frequently depend upon the type of samples being injected. For amino acid derivatives ( I ) , we inject with simultaneous flash heating and carrier gas flush. This type of injector eliminates two troublesome problems of gas chromatography. The sample can be added to the injector while it is cold and unpressurized. Under these conditions, a syringe will have little tendency to leak and the sample in the tip of the needle will not be volatilized. Al(1) G . E. Pollock and V. I. Oyama, J . Gas Chromatog., 3, 174
(1966).
Figure 1. Schematic of evaporative injector though this injector may be used in the normal manner with a septum, we recommend using the l/I6-in. Swagelok cap to obviate septal leaks and bleeding. Heating the injector can be carried out in several different ways: the injector can be flash heated by (a) resistance wire, (b) hot air from a heat gun, (c) raising a preheated block to encase the injector, (d) moving the injector into a preheated block, or (e) using focused high intensity lamps. We have used most of these techniques and have obtained good results with them; however, we prefer methods (b) and (e). Methods (a), (b), (c), and (d) are self-evident and easily designed. To our knowledge, method (e) is new; it is used with time control (Figure 2). The lamps (LI) shown in the figure are General Electric Axial Quartzline lamps, EJL 24-volt, 200 watts, 3400 OK color temperature and 25-hour life. The integral reflector is aluminum coated to reflect all wavelengths since it is supplied with a dichroic coating designed is an Agastat solid state timing to reject heat. The timer (R1) relay, Model 3732BllB, 10-ampere, 120-V ac adjustable delay from 0.5 to 15 seconds. The switch (S1) is a push button switch; 120-V ac, 10 amperes, and the adjustable autotransformer (TL) is 120-V ac, 10 amperes. The normal operating range is around 30 to 48-V ac. The temperature of the injector can be controlled by varying voltage and time of duration of the light flash. The temperature range of the ANALYTICAL CHEMISTRY, VOL. 43, NO. 8, JULY 1971
1141
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____
I
in a hydrogcn furnace using Microbraze 160. Geld plating the interior of the injector was necessary t o provide a n inert surface. Without plating, the interior becomes catalytically active and will decompose unstable compounds. The sides, 0.1 mm thick, are then spot welded to close the injector. The exterior of the injector is nickel-blackened by the Selectron process for maximum radiant heat absorption. - -
-
Figure 2. Position of injector relathe to lamps and circuitry
RESULTS AND DISCUSSION
Results obtained by addition of 20-, 30-, and 40-microliter volumes of sample to the injector, followed by solvent evaporation prior to flash heating, gave good precision, the average deviations of several compounds varying between Injection of 1-microliter sample done in triplicate 2 to and with no soIvent evaporation yielded similar average deviations, varying from 1 to 4x. 'These values indicated thai good precision as well as reproducibility could be obtained with the device. 'i'he high average deviation of was probably caused by the iong retzntion time of th: cornpound measured coupled with peak spreading and, in this casc, an old integrator was used and slope serisirivity was inadrquate for high accuracy (30 mV/sec). The derivatives evaluated were N-trifluoroacetyl aminc ~cid-2-butylesters. The column used was an OV-225, 0.020 in. i.d. X 150-ft capillary. We have fabricated injectors from glass and stainless steel with several different chamber ( B ) i)olurnes from 70 mirroliters to as high as 300 microliters and with the pot in a spherical and a cylindrical shape. This system works well in all modes. However, we ow prefer the design herein described. Naturally the lower the injector volume, the better the resolution of close peaks, This is especially noted wit.ti the derivatives which we used. Our injector with its low dead volume and flash heating gives slightly better peak resolution than the gas chromatograph original injection block.
4z.
3 m m F L A T ON FITTING INTEGRAL WITH CAVITY FOR WRENCH USE \
__
4z
HEAT
FOCdi
GG20in I D TUBING
Figure 3. Detail drawing of injector with dimensions
injector has not been completely determined, but rhermocouple measurements showed that a temperature of 500 "C could be attained in one second with the proper voltage. This would indicate that the device might be advantageously used for pyrolytic studies as well as for normal injection. Construction of the Injector. A piece of stainless steel (304) is milled as shown in Figure 3. The tubes, 0.020-in. i.d. and 0.010-in. i.d., are brazed into the stainless steel injector pot
RECEIVED f'br review February 19, 1971. Accepted April 16, 1971.
Modification of a Direct Probe Jot the Controlled Introduction o i Mass Spectrometer Samples Lee D. Smithson Air Force Materials Laboraiory JLPA), M/right-Patimon Air Force Bas?. Ohio 45433
MOSTMASS SPECTROMETERSnow come equipped with heated, direct introdiiction probes designed to introduce smiples of low volatility directly into the ion source. Because of the open design of the probes, with no provision for controlling the flow rate other than by heating, they are generally unsuitable for electrically recording the spectra of highlji volatile samples. There is a need for a technique to maintain a constant sample pressure with the direct probe inlet, not only to allow volatile samples to be r u n but to control the sample pressure of all probe samples. The modification of the probe tip described herein satisfies the need for CEC-21-110 users, and the design can perhaps be adapted for some ather spectrometers. EXPERlhlENT.4i
The inside of a commercially available silver (clr Monel) probe tip (Figure 1, Item 5 ) used with a CEC-21-110 rnaw 1142
ANALYTICAL CHEMISTRY, VOi. 43, NO. 8 , JULY 1971
spectrometer was threaded to a depth of 5 / R 2 inch to accommodate a specially fabricated, 7/3? inch long, stainless steel set screw (Item 6) ,vith eight threads. The screw acts as an adjustable plug, thus allowing the flow rate of the sample to be controlled. The head of the screw was machined to inch in form a hexagonal projection 1/16 inch long and diameter. When the screw is tight, the hexagonal projection should still project out of the sample cavity. The ion source was dismantled and the cylindrical passageway (7) to the ionizaiion chamber was electrically discharged machined to a inch deep and very slightly larger hexagonal passageway than the diameter of the hexagonal projection of the screw. A hole at the base of Ihe sample cavity of the commercially available probe tip ( 5 ) was threaded and permanently fitted with a set screw (5Aj simply to plug the hole to prevent sample from escrping from anyplace other than from around the adjustable screw ( 4 ) The ceramic insulator (3) which is standard serves as adequate shock protection; however, the little effort involved in wrapping the handle ( I ) with
